

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
  "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    
    <title>Capsules &mdash; Python v2.7.8 documentation</title>
    <link rel="stylesheet" href="../_static/default.css" type="text/css" />
    <link rel="stylesheet" href="../_static/pygments.css" type="text/css" />
    <script type="text/javascript">
      var DOCUMENTATION_OPTIONS = {
        URL_ROOT:    '../',
        VERSION:     '2.7.8',
        COLLAPSE_INDEX: false,
        FILE_SUFFIX: '.html',
        HAS_SOURCE:  true
      };
    </script>
    <script type="text/javascript" src="../_static/jquery.js"></script>
    <script type="text/javascript" src="../_static/underscore.js"></script>
    <script type="text/javascript" src="../_static/doctools.js"></script>
    <script type="text/javascript" src="../_static/sidebar.js"></script>
    <link rel="search" type="application/opensearchdescription+xml"
          title="Search within Python v2.7.8 documentation"
          href="../_static/opensearch.xml"/>
    <link rel="author" title="About these documents" href="../about.html" />
    <link rel="copyright" title="Copyright" href="../copyright.html" />
    <link rel="top" title="Python v2.7.8 documentation" href="../index.html" />
    <link rel="up" title="Concrete Objects Layer" href="concrete.html" />
    <link rel="next" title="CObjects" href="cobject.html" />
    <link rel="prev" title="Weak Reference Objects" href="weakref.html" />
    <link rel="shortcut icon" type="image/png" href="../_static/py.png" />
    <script type="text/javascript" src="../_static/copybutton.js"></script>
    
 
    

  </head>
  <body>  
    <div class="related">
      <h3>Navigation</h3>
      <ul>
        <li class="right" style="margin-right: 10px">
          <a href="../genindex.html" title="General Index"
             accesskey="I">index</a></li>
        <li class="right" >
          <a href="../py-modindex.html" title="Python Module Index"
             >modules</a> |</li>
        <li class="right" >
          <a href="cobject.html" title="CObjects"
             accesskey="N">next</a> |</li>
        <li class="right" >
          <a href="weakref.html" title="Weak Reference Objects"
             accesskey="P">previous</a> |</li>
        <li><img src="../_static/py.png" alt=""
                 style="vertical-align: middle; margin-top: -1px"/></li>
        <li><a href="http://www.python.org/">Python</a> &raquo;</li>
        <li>
          <a href="../index.html">Python v2.7.8 documentation</a> &raquo;
        </li>

          <li><a href="index.html" >Python/C API Reference Manual</a> &raquo;</li>
          <li><a href="concrete.html" accesskey="U">Concrete Objects Layer</a> &raquo;</li> 
      </ul>
    </div>    

    <div class="document">
      <div class="documentwrapper">
        <div class="bodywrapper">
          <div class="body">
            
  <div class="section" id="capsules">
<span id="id1"></span><h1>Capsules<a class="headerlink" href="#capsules" title="Permalink to this headline">¶</a></h1>
<p id="index-0">Refer to <a class="reference internal" href="../extending/extending.html#using-capsules"><em>Providing a C API for an Extension Module</em></a> for more information on using these objects.</p>
<dl class="type">
<dt id="PyCapsule">
<tt class="descname">PyCapsule</tt><a class="headerlink" href="#PyCapsule" title="Permalink to this definition">¶</a></dt>
<dd><p>This subtype of <a class="reference internal" href="structures.html#PyObject" title="PyObject"><tt class="xref c c-type docutils literal"><span class="pre">PyObject</span></tt></a> represents an opaque value, useful for C
extension modules who need to pass an opaque value (as a <tt class="xref c c-type docutils literal"><span class="pre">void*</span></tt>
pointer) through Python code to other C code.  It is often used to make a C
function pointer defined in one module available to other modules, so the
regular import mechanism can be used to access C APIs defined in dynamically
loaded modules.</p>
</dd></dl>

<dl class="type">
<dt id="PyCapsule_Destructor">
<tt class="descname">PyCapsule_Destructor</tt><a class="headerlink" href="#PyCapsule_Destructor" title="Permalink to this definition">¶</a></dt>
<dd><p>The type of a destructor callback for a capsule.  Defined as:</p>
<div class="highlight-c"><div class="highlight"><pre><span class="k">typedef</span> <span class="kt">void</span> <span class="p">(</span><span class="o">*</span><span class="n">PyCapsule_Destructor</span><span class="p">)(</span><span class="n">PyObject</span> <span class="o">*</span><span class="p">);</span>
</pre></div>
</div>
<p>See <a class="reference internal" href="#PyCapsule_New" title="PyCapsule_New"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_New()</span></tt></a> for the semantics of PyCapsule_Destructor
callbacks.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_CheckExact">
int <tt class="descname">PyCapsule_CheckExact</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*p</em><big>)</big><a class="headerlink" href="#PyCapsule_CheckExact" title="Permalink to this definition">¶</a></dt>
<dd><p>Return true if its argument is a <a class="reference internal" href="#PyCapsule" title="PyCapsule"><tt class="xref c c-type docutils literal"><span class="pre">PyCapsule</span></tt></a>.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_New">
<a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a>* <tt class="descname">PyCapsule_New</tt><big>(</big>void<em>&nbsp;*pointer</em>, const char<em>&nbsp;*name</em>, <a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em>&nbsp;destructor</em><big>)</big><a class="headerlink" href="#PyCapsule_New" title="Permalink to this definition">¶</a></dt>
<dd><em class="refcount">Return value: New reference.</em><p>Create a <a class="reference internal" href="#PyCapsule" title="PyCapsule"><tt class="xref c c-type docutils literal"><span class="pre">PyCapsule</span></tt></a> encapsulating the <em>pointer</em>.  The <em>pointer</em>
argument may not be <em>NULL</em>.</p>
<p>On failure, set an exception and return <em>NULL</em>.</p>
<p>The <em>name</em> string may either be <em>NULL</em> or a pointer to a valid C string.  If
non-<em>NULL</em>, this string must outlive the capsule.  (Though it is permitted to
free it inside the <em>destructor</em>.)</p>
<p>If the <em>destructor</em> argument is not <em>NULL</em>, it will be called with the
capsule as its argument when it is destroyed.</p>
<p>If this capsule will be stored as an attribute of a module, the <em>name</em> should
be specified as <tt class="docutils literal"><span class="pre">modulename.attributename</span></tt>.  This will enable other modules
to import the capsule using <a class="reference internal" href="#PyCapsule_Import" title="PyCapsule_Import"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Import()</span></tt></a>.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_GetPointer">
void* <tt class="descname">PyCapsule_GetPointer</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, const char<em>&nbsp;*name</em><big>)</big><a class="headerlink" href="#PyCapsule_GetPointer" title="Permalink to this definition">¶</a></dt>
<dd><p>Retrieve the <em>pointer</em> stored in the capsule.  On failure, set an exception
and return <em>NULL</em>.</p>
<p>The <em>name</em> parameter must compare exactly to the name stored in the capsule.
If the name stored in the capsule is <em>NULL</em>, the <em>name</em> passed in must also
be <em>NULL</em>.  Python uses the C function <tt class="xref c c-func docutils literal"><span class="pre">strcmp()</span></tt> to compare capsule
names.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_GetDestructor">
<a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a> <tt class="descname">PyCapsule_GetDestructor</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetDestructor" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current destructor stored in the capsule.  On failure, set an
exception and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> destructor.  This makes a <em>NULL</em>
return code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_GetContext">
void* <tt class="descname">PyCapsule_GetContext</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current context stored in the capsule.  On failure, set an
exception and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> context.  This makes a <em>NULL</em>
return code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_GetName">
const char* <tt class="descname">PyCapsule_GetName</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em><big>)</big><a class="headerlink" href="#PyCapsule_GetName" title="Permalink to this definition">¶</a></dt>
<dd><p>Return the current name stored in the capsule.  On failure, set an exception
and return <em>NULL</em>.</p>
<p>It is legal for a capsule to have a <em>NULL</em> name.  This makes a <em>NULL</em> return
code somewhat ambiguous; use <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> or
<a class="reference internal" href="exceptions.html#PyErr_Occurred" title="PyErr_Occurred"><tt class="xref c c-func docutils literal"><span class="pre">PyErr_Occurred()</span></tt></a> to disambiguate.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_Import">
void* <tt class="descname">PyCapsule_Import</tt><big>(</big>const char<em>&nbsp;*name</em>, int<em>&nbsp;no_block</em><big>)</big><a class="headerlink" href="#PyCapsule_Import" title="Permalink to this definition">¶</a></dt>
<dd><p>Import a pointer to a C object from a capsule attribute in a module.  The
<em>name</em> parameter should specify the full name to the attribute, as in
<tt class="docutils literal"><span class="pre">module.attribute</span></tt>.  The <em>name</em> stored in the capsule must match this
string exactly.  If <em>no_block</em> is true, import the module without blocking
(using <a class="reference internal" href="import.html#PyImport_ImportModuleNoBlock" title="PyImport_ImportModuleNoBlock"><tt class="xref c c-func docutils literal"><span class="pre">PyImport_ImportModuleNoBlock()</span></tt></a>).  If <em>no_block</em> is false,
import the module conventionally (using <a class="reference internal" href="import.html#PyImport_ImportModule" title="PyImport_ImportModule"><tt class="xref c c-func docutils literal"><span class="pre">PyImport_ImportModule()</span></tt></a>).</p>
<p>Return the capsule&#8217;s internal <em>pointer</em> on success.  On failure, set an
exception and return <em>NULL</em>.  However, if <a class="reference internal" href="#PyCapsule_Import" title="PyCapsule_Import"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Import()</span></tt></a> failed to
import the module, and <em>no_block</em> was true, no exception is set.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_IsValid">
int <tt class="descname">PyCapsule_IsValid</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, const char<em>&nbsp;*name</em><big>)</big><a class="headerlink" href="#PyCapsule_IsValid" title="Permalink to this definition">¶</a></dt>
<dd><p>Determines whether or not <em>capsule</em> is a valid capsule.  A valid capsule is
non-<em>NULL</em>, passes <a class="reference internal" href="#PyCapsule_CheckExact" title="PyCapsule_CheckExact"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_CheckExact()</span></tt></a>, has a non-<em>NULL</em> pointer
stored in it, and its internal name matches the <em>name</em> parameter.  (See
<a class="reference internal" href="#PyCapsule_GetPointer" title="PyCapsule_GetPointer"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_GetPointer()</span></tt></a> for information on how capsule names are
compared.)</p>
<p>In other words, if <a class="reference internal" href="#PyCapsule_IsValid" title="PyCapsule_IsValid"><tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_IsValid()</span></tt></a> returns a true value, calls to
any of the accessors (any function starting with <tt class="xref c c-func docutils literal"><span class="pre">PyCapsule_Get()</span></tt>) are
guaranteed to succeed.</p>
<p>Return a nonzero value if the object is valid and matches the name passed in.
Return 0 otherwise.  This function will not fail.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_SetContext">
int <tt class="descname">PyCapsule_SetContext</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, void<em>&nbsp;*context</em><big>)</big><a class="headerlink" href="#PyCapsule_SetContext" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the context pointer inside <em>capsule</em> to <em>context</em>.</p>
<p>Return 0 on success.  Return nonzero and set an exception on failure.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_SetDestructor">
int <tt class="descname">PyCapsule_SetDestructor</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, <a class="reference internal" href="#PyCapsule_Destructor" title="PyCapsule_Destructor">PyCapsule_Destructor</a><em>&nbsp;destructor</em><big>)</big><a class="headerlink" href="#PyCapsule_SetDestructor" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the destructor inside <em>capsule</em> to <em>destructor</em>.</p>
<p>Return 0 on success.  Return nonzero and set an exception on failure.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_SetName">
int <tt class="descname">PyCapsule_SetName</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, const char<em>&nbsp;*name</em><big>)</big><a class="headerlink" href="#PyCapsule_SetName" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the name inside <em>capsule</em> to <em>name</em>.  If non-<em>NULL</em>, the name must
outlive the capsule.  If the previous <em>name</em> stored in the capsule was not
<em>NULL</em>, no attempt is made to free it.</p>
<p>Return 0 on success.  Return nonzero and set an exception on failure.</p>
</dd></dl>

<dl class="function">
<dt id="PyCapsule_SetPointer">
int <tt class="descname">PyCapsule_SetPointer</tt><big>(</big><a class="reference internal" href="structures.html#PyObject" title="PyObject">PyObject</a><em>&nbsp;*capsule</em>, void<em>&nbsp;*pointer</em><big>)</big><a class="headerlink" href="#PyCapsule_SetPointer" title="Permalink to this definition">¶</a></dt>
<dd><p>Set the void pointer inside <em>capsule</em> to <em>pointer</em>.  The pointer may not be
<em>NULL</em>.</p>
<p>Return 0 on success.  Return nonzero and set an exception on failure.</p>
</dd></dl>

</div>


          </div>
        </div>
      </div>
      <div class="sphinxsidebar">
        <div class="sphinxsidebarwrapper">
  <h4>Previous topic</h4>
  <p class="topless"><a href="weakref.html"
                        title="previous chapter">Weak Reference Objects</a></p>
  <h4>Next topic</h4>
  <p class="topless"><a href="cobject.html"
                        title="next chapter">CObjects</a></p>
<h3>This Page</h3>
<ul class="this-page-menu">
  <li><a href="../bugs.html">Report a Bug</a></li>
  <li><a href="../_sources/c-api/capsule.txt"
         rel="nofollow">Show Source</a></li>
</ul>

<div id="searchbox" style="display: none">
  <h3>Quick search</h3>
    <form class="search" action="../search.html" method="get">
      <input type="text" name="q" size="18" />
      <input type="submit" value="Go" />
      <input type="hidden" name="check_keywords" value="yes" />
      <input type="hidden" name="area" value="default" />
    </form>
    <p class="searchtip" style="font-size: 90%">
    Enter search terms or a module, class or function name.
    </p>
</div>
<script type="text/javascript">$('#searchbox').show(0);</script>
        </div>
      </div>
      <div class="clearer"></div>
    </div>  
    <div class="related">
      <h3>Navigation</h3>
      <ul>
        <li class="right" style="margin-right: 10px">
          <a href="../genindex.html" title="General Index"
             >index</a></li>
        <li class="right" >
          <a href="../py-modindex.html" title="Python Module Index"
             >modules</a> |</li>
        <li class="right" >
          <a href="cobject.html" title="CObjects"
             >next</a> |</li>
        <li class="right" >
          <a href="weakref.html" title="Weak Reference Objects"
             >previous</a> |</li>
        <li><img src="../_static/py.png" alt=""
                 style="vertical-align: middle; margin-top: -1px"/></li>
        <li><a href="http://www.python.org/">Python</a> &raquo;</li>
        <li>
          <a href="../index.html">Python v2.7.8 documentation</a> &raquo;
        </li>

          <li><a href="index.html" >Python/C API Reference Manual</a> &raquo;</li>
          <li><a href="concrete.html" >Concrete Objects Layer</a> &raquo;</li> 
      </ul>
    </div>  
    <div class="footer">
    &copy; <a href="../copyright.html">Copyright</a> 1990-2014, Python Software Foundation.
    <br />
    The Python Software Foundation is a non-profit corporation.
    <a href="http://www.python.org/psf/donations/">Please donate.</a>
    <br />
    Last updated on Jun 29, 2014.
    <a href="../bugs.html">Found a bug</a>?
    <br />
    Created using <a href="http://sphinx.pocoo.org/">Sphinx</a> 1.0.7.
    </div>

  </body>
</html>